
where \(\mu _i \propto \sigma _i \sqrt{ M_{i} \log (M_{i})}\)  is the regularization term of the atomic norm penalty. This problem can be efficiently solved using the Matlab CVX toolbox [1]}. Unlike the overcomplete dictionary, let alone the dictionary's undercomplete counterpart, in Orthogonal Matching Pursuit (OMP), since the number of atoms in (REF ) is infinite, high accuracy recovery of \({\mathbf {h}}_i\)  can be achieved by well controlling the regularization term \(\mu _i\) . The computational complexity in this stage is \(O\big (M_i^{3.5}\big )\)  [2]}. After getting the estimate of \({\mathbf {h}}_i\) , denoted henceforth as \(\hat{{\mathbf {h}}}_i\) , from (REF ), we can extract its angular parameters, e.g., via the subspace-oriented root MUSIC algorithm  [3]}, as detailed in the next subsection.
